Defining the freedom to do otherwise

Arminians speak of the freedom to do otherwise as if that were a transparent concept. But it’s actually quite tricky to pin down. Here are some popular, but defective, attempts to explicate the concept:

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Suppose a certain person in fact did not go to Boston this morning, but suppose it seems that he could have done so. We want to say that though he stayed in Providence, he could have done otherwise — he could have gone to Boston. Surely the statement that he could have done otherwise does not mean merely that it is logically possible that he did otherwise, for superhuman and miraculous bits of behavior are logically possible. But we don't want to say, of a person who failed to perform a miracle, that he could have done otherwise. Nor does our statement mean that it is epistemically possible that the person did otherwise. In a case where we lack information about what a person might have done, we may say that it is epistemically possible for us that he did otherwise. This is consistent with its being the case that his performance of his actual act was entirely necessary and unavoidable.

Some have said that ‘can’s are constitutionally iffy. On a simple version of this view, to say that someone could have done otherwise is just to say that if he had chosen to do otherwise, then he would have done otherwise. Chisholm points out ([P&O], 56–7) two reasons why this is wrong. First, suppose the person was capable of traveling in any direction and easily could have gone to Boston; but suppose in addition that he did not know the way to Boston. If he had chosen to go to Boston, he would have ended up in New London. Then it is correct to say that he could have gone to Boston, but incorrect to say that if he had chosen to go to Boston, he would have done so. Secondly, suppose the person is incapable of choosing to go to Boston. Maybe he is overwhelmed with fear of Boston. But if nothing else prevents the trip, it will be correct to say that if he had chosen to go to Boston, he would have gone, but it is incorrect to say that he could have gone to Boston.

Another account of ‘could have done otherwise’ makes use of the concept of sufficient antecedent causal condition. We might think that when we say that someone could have gone to Boston instead of staying in Providence, what we mean is merely that at some earlier time this morning, his trip to Boston was causally indeterminate — there was no sufficient causal condition either for his going to Boston or for his not going to Boston. Chisholm argues against this idea, too. Suppose another person was lying in wait in Chelmsford. Suppose this other person would have freely interfered with our man's travel plans if he had tried to get to Boston. Then it would not be correct to say that the man could have gone to Boston, but it would have been correct to say that there was no sufficient causal condition then in place that would have prevented the trip.

http://plato.stanford.edu/entries/chisholm/#MetIIAgeFreWilPro